Project Summary/Abstract Proteasome inhibition in mammalian cells results in transcriptional upregulation of proteasome genes, thereby providing the cell with a homeostatic control mechanism to maintain proteasome levels. Preliminary studies indicated that this response was mediated by the transcription factor Nrf1 (also called Nfe2l1) and that knockdown of this factor sensitized cancer cells to proteasome inhibitor treatments. The overall goal of the current proposal is to further understand the mechanism behind this proteasome homeostatic pathway and to evaluate if inhibition of this pathway could be a viable anti-cancer strategy in vivo, especially when used in conjunction with proteasome inhibitors. Specific Aims during the mentored phase are designed to understand the mechanism of Nrf1 activation following proteasome inhibition and to evaluate the utility of depleting Nrf1 in the treatment of mouse xenograft tumors with covalent proteasome inhibitors. Specific Aims during the independent phase are designed to understand the role of p97/VCP and its co-factors in Nrf1 activation and to identify novel chemical inhibitors of the Nrf1-mediated proteasome recovery pathway. The proposed work has the potential to shed light on the functioning of the proteasome recovery pathway and also suggest strategies for the development of novel anti-cancer therapeutics that target the ubiquitin- proteasome system.